1940 Popular Science One Tube TRF


Seventy-five years ago this month, Popular Science (November 1940) carried the plans for this one-tube loudspeaker set for the broadcast band.  While it’s technically a one-tube set, it actually has two stages, since it employs a dual pentode, the 1E7G.  One half of the tube acts as an RF amplifier, with the other half serving as detector and AF amplifier.

1955NovPSschematicWith a good outdoor antenna, the set was said to provide good reception on all local stations. With a station ten miles away, and indoor antenna could be used. It had good selectivity such that powerful stations just 30 kc apart could be easily separated.

Since it was a TRF set, it employed two tuning condensers. The first tuned in the RF amplifier stage, with the second one serving as the main tuning condenser. The set’s volume was adjusted by a rheostat adjusting the filament voltage of the AF amplifier stage.

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